It has been recognized in the prior art that it is desirable to stop bleeding by applying materials to the wound or tissue which initiate or enhance blood coagulation. Such materials have included liquid glues (cyanoacrylate adhesives, gelatinous glues, UV curable polymers, etc.). Other materials which are made from human or animal blood components have been used but therefore are expensive to manufacture.
One method used to reduce bleeding involves initiating or accelerate blood clotting by applying hygroscopic porous particles directly to a wound. In this method the porous particles absorb the water from blood allowing the natural fibrinogens within the blood to coagulate, which results in a blood clot. The pore size of such particles should be such that water is able to be readily adsorbed by the particles, but the clot forming blood components (thrombin, fibrinogen, fibrin, platelets, etc.) are not. The size of the pores, therefore, should be less than 1 micrometer (1,000 nm) and preferably less than 0.1 micrometer (100 nm). The particles may be made of many different materials, although it is preferable that the materials be biocompatible and eventually absorbed by the body. Another method is described in U.S. Pat. No. 4,822,349 (Hursey) which describes the use of zeolites, or molecular sieves, for accelerating clotting. The zeolites are used in a particle form either as a powder poured onto or into a wound, or embedded in a wound dressing. However, while effective at adsorbing water from the blood and stopping bleeding, this method suffers from several major problems. Zeolites are inorganic and are not readily adsorbed by the body which creates significant difficulties in caring for the wound once the bleeding is stopped. The zeolite particles, which have been placed in the wound, must be debrided or scraped out of the wound once the bleeding has stopped. This can be very painful for the trauma victim. There is also a strong exothermic reaction when water is adsorbed into zeolites that can cause the temperatures at the wound site to reach 40° C. to 50° C. or higher which can burn the patient. Also a significant number of people can have allergic reactions to the zeolites. Another major concern is that the loose zeolite particles can become entrained in a blood vessel where they will continue to promote formation of clots. These small clots, which can then circulate in the blood system, can potentially cause embolisms, strokes, or other clot related problems. The U.S. Pat. No. 6,060,461 (Drake) describes the use of particles made of porous materials from within the classes of polysaccharides, cellulosics, polymers (natural and synthetic), inorganic oxides, ceramics, zeolites, glasses, metals and composites.
Polysaccharides are preferred because of their ready availability and modest cost. They are widely known to be biocompatible and are readily absorbed by the body over time. Polysaccharides can be provided as starch, cellulose, and even chitin. Chitin based wound dressings are provided under the trade name “Hemcon” and comprise chitin particles (from shrimp) embedded in a wound dressing. The particles can be applied in a powder form directly to the wound, or held in place on the wound. However, powders are difficult to apply, especially to wounds in which blood is flowing since the powders can be washed away with the flowing blood before clotting can be initiated.
A solution to problem of the powders washing away is described in the Hursey and Drake patents wherein they embed or attach the powders to a wound dressing. The wound dressing can take the form of a sheet or film in which the particles are adhered to or to the surface of fibers which make up woven or non-woven gauze-like fabric or sheet. The particles can also be interspersed with fibers, filaments or other particles in a self supporting structure, entangled within the fibrous elements of a net, web, fabric or sheet. However, both the biocompatible particles and the zeolite particles suffer the same problem in that they can become entrained in the blood vessels and cause clotting related problems in the blood vessels. While both of the Hursey and Drake patents describe the use of a dressing with the particles embedded or attached to a dressing for ease of application, there still exists the danger of the particles shedding from dressing and becoming entrained in the blood vessel and causing clotting within a blood vessel. In addition, the use of a dressing made of one material combined with the particles made of a different material increases problems of biocompatibility and absorption. It also increases the complexity of manufacturing and consequently manufacturing costs. The U.S. Pat. No. 3,620,218 (Schmitt) discloses a felt made of polyglycolic acid fibers which may be used as a hemostat. However, the felted fibers can float from a bleeding surface and are generally too porous.
The U.S. Pat. No. 3,937,223 (Roth) discloses an improvement upon 3,620,218 by compaction of the felt on at least one side to provide strength and rigidity to the felt as well as providing a smoother surface which can be drawn into close conformity to the wound and thus reduce pockets in the felt where blood or other fluids can accumulate. Roth uses filaments of about 0.5 to 12 deniers per filament (approximately 7 um to 34 um) and, conveniently, 2 to 6 deniers (approximately 14 um to 24 um) per filament. These fibers are quite large and stiff which creates large pores when made into a felt. To reduce the large pores one compresses the felt to smoothen the surface of the felt and to press the filaments closer together to create smaller pores between the fibers and thereby enhance hemostatic properties of the felt. However, even after compaction this technique suffers from the large open regions or void volume. When the filaments are compressed together, the void volume, or amount of open area between fibers, is greatly reduced. The amount of open area between fibers is important as the open area allows water to be wicked between the fibers, leaving behind platelets and other clotting agents, thus initiating the clotting process. The void volumes in compressed and calendared felts are typically less than 70% and usually less than 50%. The low void volumes in the felt reduces the hemostatic effectiveness of the compressed felts since the wicking of the water from the blood is a function of the surface area of fibers in contact with the blood and the capillary effect created by the pore size as well as the number of pores in the surface of the media. In addition, to the less than optimal hemostatic properties, the fibers in the felt which have not been compacted or embossed are not bonded to the other fibers.
In contrast to the prior art the present invention is to provide a biocompatible wound dressing which promotes clotting, reduces the risk of clot-promoting particles from entering the bloodstream, is easy to use, and is cost-effective to manufacture.